class Solution:
    def isInterleave(self, s1: str, s2: str, s3: str) -> bool:
        len1, len2, len3 = len(s1), len(s2), len(s3)
        if (len1 + len2 != len3):
            return False
        dp = [[False] * (len2 + 1) for i in range(len1 + 1)]
        dp[0][0] = True
        for i in range(1, len1 + 1):
            dp[i][0] = (dp[i - 1][0] and s1[i - 1] == s3[i - 1])
        for j in range(1, len2 + 1):
            dp[0][j] = (dp[0][j - 1] and s2[j - 1] == s3[j - 1])
        for i in range(1, len1 + 1):
            for j in range(1, len2 + 1):
                dp[i][j] = (dp[i - 1][j] and s1[i - 1] == s3[i + j - 1]) or (dp[i][j - 1] and s2[j - 1] == s3[i + j - 1])
        return dp[-1][-1]